The present subject matter generally concerns a coupling capacitor for use in conjunction with components and signal connections in a printed circuit board (PCB) environment. At least two capacitor structures are provided in a single monolithic device to form a transmission line capacitor in accordance with the present subject matter.
A transmission line is generally defined as two or more parallel conductors used to connect a source to a load. Such terminology often conjures thoughts of power generation and distribution systems that utilize large-scale transmission lines to transport electrical energy among multiple sources and loads of a power network. However, transmission lines are not only utilized in large-scale environments; in fact, even the smallest electrical applications often employ transmission line configurations for energy distribution. An example of a particular such application, generally the focus of the present subject matter, corresponds to transmission lines that are implemented on a printed circuit board (PCB) environment by parallel signal traces that connect various components or connection points.
PCB “transmission lines” have proven quite useful for many conventional circuit applications, especially those utilizing relatively high frequency signals. However, high-frequency signals traveling in such a fashion may be readily susceptible to a variety of undesirable signal-altering phenomena, including noise spikes that can alter signal data and cause data errors as well as impedance variations in a signal path that can cause signal reflections.
Capacitors are often used to help regulate a transmitted signal and ensure that undesirable signal-altering phenomena is minimized. For many applications, capacitors are desirable that have the biasing capability for blocking DC components of a transmitted signal and the coupling capability for passing AC voltage components (often the “data” portion of a signal.) Such capacitors will be hereafter referred to as coupling capacitors, and should be distinguished from decoupling capacitors which typically block AC signal propagation. Coupling and decoupling of transmitted signals often becomes even more important when such transmitted signals are characterized by relatively high frequencies. Examples of capacitor technology for use in accordance with high frequency signaling applications are disclosed in U.S. Pat. No. 6,272,003 B1 (Schaper) and U.S. Pat. No. 6,023,408 (Schaper).
A coupling capacitor in a transmission line environment may require unique design considerations. Transmission lines are typically characterized by a certain impedance, which is preferably maintained in as constant a fashion as possible along the signal traces that form each respective signal transmission path. Maintaining a relatively constant transmission line impedance helps to ensure signal integrity.
Determination and preservation of certain capacitor performance characteristics is often addressed by the selection of materials used in such devices. As known in the art, multilayer capacitors typically comprise materials for forming at least two major physical structures, the conductive electrode plates and adjacent dielectric portions. Particularly, the selection of dielectric materials for use in capacitor devices can greatly affect component design and functionality due to availability of dielectrics with a wide range of different dielectric constants (K).
Examples of electronic devices that employ materials with relatively high dielectric constants for selected component features include U.S. Pat. No. 6,275,370 B2 (Gnade et al.), U.S. Pat. No. 5,883,781 (Yamamichi et al.), U.S. Pat. No. 4,853,827 (Hernandez), U.S. Pat. No. 4,464,701 (Roberts et al.), U.S. Pat. No. 3,883,784 (Peek et al.), and Japanese Patent No. JP6290984 (Kuroiwa et al.).
Many electronic devices, particularly capacitive structures, employ a combination of materials with different dielectric constants in a single structure. Such combination of dielectric materials may often yield a device with a wider range of functionality or given performance characteristic(s). U.S. Pat. No. 5,779,379 (Galvagni et al.), U.S. Pat. No. 5,517,385 (Galvagni et al.), U.S. Pat. No. 6,108,191 (Bruchhaus et al.), U.S. Pat. No. 6,072,690 (Faroog et al.) and Japanese Patent No. JP1189997A (Takaaki et al.) disclose exemplary electronic devices that incorporate different dielectric materials. Similarly, U.S. Pat. No. 3,210,607 (Flanagan) provides an example of an apparatus with different ferromagnetic materials provided therewith.
Yet another reference disclosing aspects of the formation of capacitive structures utilizing different dielectric materials is U.S. Pat. No. 5,583,738 (Kohno et al.). Such reference provides for a capacitor array with distinct capacitive units separated from each other by a layer having a lower dielectric constant than that of the material used in the capacitive units themselves. Such disclosed capacitive structure may be suitable for use in a printed circuit board environment.
Additional background references that address aspects of capacitor design and/or related selection of dielectric materials include U.S. Pat. No. 6,300,267 B1 (Chen et al.), U.S. Pat. No. 6,208,501 B1 (Ingalls et al.), U.S. Pat. No. 6,111,744 (Doan), U.S. Pat. No. 6,094,335 (Early), U.S. Pat. No. 5,561,586 (Tomohiro et al.), and U.S. Pat. No. 3,699,620 (Asher et al.).
While various aspects and alternative features are known in the field of chip-type capacitors and dielectric portions thereof, no one design has emerged that generally addresses all of the issues as discussed herein. The disclosures of all the foregoing United States patents are hereby fully incorporated into this application for all purposes by reference thereto.